Electrical discharge device having cavity resonators



C. B. HORSLEY ELECTRICAL DISCHARGE DEVICE HAVING CAVITY RESONATORS Filed April 27, 1944 Jan. 4, 1949.

ATTORNEY$ Patented Jan. 4, 1949 ELECTRICAL DISCHARGE DEVICE HAVING CAVITY RESONATORS Caperton B. Horsley, Stamford, Conn., assignor to Machlett Laboratories Incorporated, Springdale, Conn, a corporation of Connecticut Application April 2-7, 1944, Serial No. 532,946

10 Claims.

This invention relates to electrical discharge devices adapted for ultra-high frequency use and of the type in which a beam of charged particlesis subjected to the action of an alternating electric field. More particularly, the invention is concerned with a novel electric discharge device, which may be employed as an ultra-high frequency oscillator or amplifier and can be operated safely at higher output rates than prior devices for the same purpose.

At the present time, electron discharge devices functioning in accordance with the principle of velocity modulation are well known and, in such devices as the Klystron, an electron beam from a source passes through aligned openings, usually containing grids, in opposite walls of a cavity resonator in which the beam is subjected to the action of an alternating field produced by oscillations within the resonator. The dimensions of the resonator and the frequency of the oscillations therein are such that, in their passage between the grids, some of the electrons are accelerated, others are decelerated, while still others may leave with their velocity substantially unchanged. Beyond the resonator, the electrons enter a fieldfree space termed-a drift tube and in their passage through the tube the differences in thevelocities of the electrons cause them to become bunched. The bunches of electrons pass from the drift tube through a grid into a second cavity resonator which resonates preferably at the same frequency as the first, and, in the second resonator, the bunches of electrons set up an alternating field from which energy may be absorbed. If the device is employed as an oscillator, some of the absorbed energy is fed back to the first resonator to maintain the field therein, while, if the device is used as an amplifier the field in the first resonator is maintained by energy from the signal to be amplified and the energy absorbed from the second resonator passes to an output circuit.

In such a velocity modulation device, the resonators and the drift tube are all at the same D. C. potential and the electrons in the beam receive the major part of their acceleration before they enter the first or buncher resonator and they are not accelerated in the space between the resonators. The resonators have small openings, so that their efiiciency may not be too greatly impaired, and the grids, when used in the openings, provide the desired close coupling between the beam and the resonators. Since the beam will burn out any grid through which it passes if the current density of the beam is too great and the electron speed too high, the beam' passing through the first resonator must be restricted astoeither tect the grids.

Some of the limitations upon the prior devices arise from space charge effects. As is well known, it is difilcult to maintain a beam of charged par ticles, which is of small diameter, high intensity, and substantial length. Such a beam may be focused at one point along its axis to limit its diameter, but, as the beam travels along, it tends to expand because of the space charge effect.'

This tendency assumes considerable importance in prior devices.

The present invention is directed to the provision of a novel electric discharge device capable of use as an oscillator or amplifier, which, although involving the use of a beam of charged particles, functions differently. from and is superior to velocity modulation devices of the type above described. In its broadest aspect, the new device includes a source of charged particles, means for intermittently cutting off the flow of particles so'that the particles are grouped, means for accelerating the groups of particles, and means for retarding, and thereby absorbing energy from the groups of accelerated particles. Preferably, the charged particles employed are electrons and the means for cutting oif the fiow thereof is an al-- ternating field within a cavity resonator. yond the resonator, the groups of electrons produced by the action of the field on the electron beam are accelerated by an electrode or a series of electrodes spaced along the path of travel of the electron groups and maintained at proper potentials. After having thus been accelerated, the electron groups are focused by appropriate means and directed into a second cavity resonator in which they set up an alternating field from which energy is absorbed. Since the beam of electrons enters the first resonator at relatively low velocity, grids may be mounted in the openings in the resonator without danger of being burned out, even though the beam is of high current density. The grouping of the electrons takes place wholly within the first resonator and it is possible to accelerate the groups in the space between the two resonators and also to focus the groups immediately prior to their entering the second resonator. The groups, accordingly, enter the second resonator at high velocity and high current density, so that a correspondingly large amount of energy may be absorbed from the alternating field which they set up within the second resonator. At the same time, the possibility of focusing the groups about to enter the second resonator permits the use of a small opening into the second resonator with resultant increase in efliciency and without the necessity of employing a grid in the opening to obtain close coupling.

For a better understanding of the invention, reference may be had to the accompanying drawing in which the single figure is a-partly diagrammatic longitudinal sectional view of an embodiseveral leads pass through a press sealed in the end wall 8 of the section i.

A tubular metal section 9 is sealedat one end on the cylindrical end of the section! and within the metal section is a cavity resonator ill, which has parallel walls H, H lying at right angles to the axis of electrodefi and formed with. openings aligned with that electrode'and con taining grids l3, l4,respective1y. The resonator has a peripheral opening fi aligned with 'a'sirn; ilar opening it through the Wall of section 9;"and a coupling loop 11 lies within the resonator and has a lead it, which extends through a conical connection l9 and through an insulatingsupport to terminate as a probe .2! within" a hollow wave guide 22.

The other end of the metal section 9 is'sealed on a cylindrical glass section 23 at one end of a chamber generally designated 24 and formed.ofy alternate glass sections 23 and annular metal discs 25. The discs are of such dimensions as to project beyond the glass sections both inwardly and outwardly, and the glass sections and discs are aligned to produce a tubular structure axially aligned with the openings through walls H, l2 of the cavity H]. ,The several discs serve "as ac-j celerating electrodes and they are provided with, leads 2'6 connected to space points on a voltage; dividing resistor generally designated '21. A, This resistor is provided with a selector switch, con ventionally indicated at 28, which may bensed for phasing purposes. At the end of the, insulating structure remote from the resonator i0, the'structure is connected to atubular metal sectiondfi, the open end of which is closed by a cavity resonator 30,'which is similar to resonator i0 and resonates at the same frequency. The resonator has parallel walls 3|, 32 lying transverse to the aXis of the device, and wall 3| contains a small centralopening 33. A focusing electrode 3 !v is mounted on the outside of wall 3i around opening 33v andthe adjacent disc 35 .withinthe structure is formed with a smaller central opening than the other discs and cooperates for focusing purposes with the electrode 3d. I M I n Resonator 30 is formed with a peripheral opening 36 aligned with an opening 36a through the wall of section 29, and the resonator contains an output coupling loop 31, the end of whichiprojects through openin 36 and through a conical connection 38 to pass through. an insulating supe port 39 and terminate as a probe 40 within a hollow wave guide ll. The leads of. filament. 2

3 .are connected to a voltage source 42, and lead 5 of the focusing elec-. trode 4 is connected to the negative side of a voltage source 43. Lead i of accelerating electrode 6 is connected tothe positive side ofa voltage source 44. A voltage source is connected across the resistor 21, and the negative side of the source is connected by connection 46 to the metallic section 9, and through it, to the resonator H]. The several discs 25 are connected to taps "on the resistor and'thefocusing disc 35 is connected to the positive side of the voltage source 45 by a connection 4?. The focusing electrode 34 is connected to the negative side of a voltage source 88, provided for that focusing purpose, by a connection leading to the cylindrical section 29, with which electrode 34 is in electrical connection through the wall of cavity 30. The positive side of source 48 is connected to the positive side of resistor 21?.

In the operation of the device as an amplifier, the filament is heated and emits electrons, which are focused by electrode 4 to form a beam and are accelerated by electrode t to a relatively low velocity. The signal to be amplified is applied to the wave guide 22 and the resonators ill and- 30 may be adjusted by conventional means not shown so that they will resonateat thefrequency of the si nal.-

7 The coupling loop ll then functions in response to the signal to cause resonator ii) to resonate. The electrical values employed are so chosen that the alternating electric potential between the grids I3 and i l of resonator ID is high relative to the voltage'represented by the speed of the electrons entering the resonator and, as a consequence, the potential between the grids acts during one half cycle'to prevent substantially all fiow of electrons through the resonator, while permitting the'electrohs t'o'erner'ge from the resonator into the structure 25 during thenext half cycle. The'electrons will, accord ingly, enter the structure 24 in the form of groups 7 and thebeam made up of the groups Will-be ac-f; celerated by' the successively. higher poten ti'als applied to the electrodes 25. At the end of the chamber 24, thebearn is focused by the action of electrodes 34 and35 energized by thevoltage source 48.

The groups of electrons leaving chamber 24 enter the second cavity resonator 3o through'the' opening 33. This resonator resonates at the same frequency as cavity Ill and the passage of the.

groups of electrons across resonator'3fl frornthe opening to theirpoint of impingement on the end wall 32 of the resonator causes the latterto resonate. The alternatingfleld within resonator 3B retards the electrons, so that energy is given up to the resonatorby the electrons and is then transmitted by the couplin loop 37 to the output wave guide 4i.

From the foregoing,

As distinguished from prior practice, the ;electron beam enters the first resonator of the de vice at relatively low velocity and may, there,- fore, be of relatively high current density with out danger of burning out the grids in the resonator openings. v takes place wholly within the first resonator, and no drift tube, .within which .bunching pr electrons of different velocitymay take place, is required. The two, resonators are electrically separated and the chamber between them insulates them from. one another and defines the space in which thebeam may be subjected to accelerating potentials. Within .the chamber, the beam made upof. groups of electrons is given a high velocity and at theexit end of the cham t win be app rent that" the new device differs from prior devices for the same general purpose in numerous respects;

The grouping of the electrons] the second resonator may be small and, accordingly, no grid in the opening is necessary to maintain the desired close coupling between the beam and resonator. Also, since no grid used, the speed of the electrons and the intensity of the beam may be much higher than would be permissible, if a grid were present.

The most desirable spacing of grids l3, M, the size of the opening 33, the values of the several voltage sources, and similar features depend on the frequency at which the device is to operate, the output desired, and various considerations of that sort. In general, however, it may be said that the operation of the device improves as frequency is increased. The specific construction illustrated is a desirable physical embodiment of the invention, but devices of other constructions operating on the same principles will readily occur to those familiar with such apparatus.

I claim:

1. An electrical discharge device adapted for ultra-high frequency use, which comprises an evacuated envelope, means within the envelope for producing a beam of charged particles traveling along a rectilinear path within the envelope at relatively low velocity, means within the envelope defining a cavity resonator having aligned openings through which the particles pass, means for maintaining an oscillating field within the resonator which acts on the beam to cause the particles to be formed into groups, means, for subjecting the particles traveling through the envelope beyond the resonator to a constant rectilinear field to accelerate the groups of particleswithout substantially changing their direction, said means including a plurality of electrodes distributed within the envelope along the path of the particles, potential-source means connected to said electrodes for maintaining them at increasing potentials with respect to the beam-producing means, and means within the envelope in the path of travel of the particles beyond the group accelerating means for absorbing energy from the accelerated groups, said absorbing means including a cavity resonator having an opening through which the groups pass into the resonator.

2. An electrical discharge device adapted for ultra-high frequency use, which comprises an evacuated envelope, means within the envelope for producing groups of charged particles traveling at relatively low velocity along a rectilinear path, means within the envelope for subjecting the groups of particles moving along said path to a constant rectilinear field to accelerate the groups without substantially changing their direction, said means including a plurality of, electrodes distributed within the envelope along the path of the particles, potential-sourcemeans connected to said electrodes for maintaining them at increasing potentials with respect to the means for producing the groups of charged particles, and means Within the envelope beyond the electrodes and spaced therefrom for absorbing energy from the accelerated groups of particles, said absorbing means including a cavity resonator having an opening through which the groups of particles may enter the resonator.

3. An electrical discharge device adapted. for ultra-high frequency use, which comprises an evacuated envelope, means within the envelope for producing a beam of charged particles'traveling along a rectilinear path within the envelope at relatively low velocity, a cavity resonator mounted on the envelope wall and having walls extending across the path of the beam, the resonator Walls having aligned openings through which the beam may pass, a second cavity resonator mounted on the envelope wall and having at least one Wall extending across the path of the beam, said resonator wall having an opening through which the beam may enter the resonator, means for maintaining an oscillating field Within the first resonator which is adapted to act on the beam passing through the resonator to cause the particles to be formed into groups, and means for subjecting the groups of particles to a constant rectilinear-field to accelerate the groups without substantially changing their direction including a plurality of electrodes mounted on the envelope wall and spaced along the path of the groups of particles between the resonators and potential-source means connected to said electrodes for maintaining them at increasing potentials with respect to the beamproducing means.

4. Anelectrical discharge device adapted for ultra-high 'frequency use, which comprises an evacuated envelope, means within the envelope for producing a beam of charged particles traveling along a rectilinear path Within the envelope at relatively low velocity, a cavity resonator mounted on the envelope Wall and having walls extending across the path of the beam, the-resonator walls having aligned openings through which the beam may pass, a second cavity resonator mounted on the envelope wall and having at least one wall extending across the path of the beam, said resonator wall having an opening through which the beam may enter the resonator, means for maintaining an oscillating field within the first resonator which. is adapted to act on the beam passing through the resonator to cause the particles to be formed into groups, means for subjecting the groups of particles to a constant rectilinear field to accelerate the groups Without substantially changing their direction including a plurality of electrodes mounted on the envelope wall and spaced along the path of the groups of particles between the resonators, and potential-source means connected to said electrodes for maintaining them at increasing potentials with respect to the beam-producing means, and means for focusing the accelerated groups of particles approaching the opening into the secondresonator.

5. vAn electrical discharge device adapted for ultra-high frequency use, which comprises an evacuated envelope, means within the envelope for producing a beam of charged particles travelingalong a rectilinear path within the envelope at relatively low velocity, a cavity resonator mounted on the envelope wall and having walls extending across the path of the beam, the resonator walls having alignedopenings through which the beam may pass, a second cavity resonator mounted on the envelope walland having at least one wall extending across the path of the. beam, said resonator wall having an opening through which the beam may enter the resonator, means for maintaining anoscillating field within the first resonator which is adapted to act on the beam passing through the resonator to cause the particles to be formed into groups, and a plurality of electrodes within the envelope distributed along the space between the resonators, potential-source means connected to said electrodes :for maintaining them at increasing potentials withi respect toi the beanrproducingj means effective to subject the groups of particles to": a constant mectilinear fi'eld whichi accelerates the groups without substantially changing their direction. I

6. An electrical discharge"device-adapted for.

respect to the means for producing the groups of charged particles, means within the" envelope beyond the "accelerating means and spaced therefrom for absorbing energy from'the accelerated groups of particles, said"absorbing means in cluding a cavity resonator having an opening throughwhic'h the groups of particles may enter the resonator, andmeans within the envelope for focusingthe'accelerated groups of particles as they approach the opening in 'thed'esonator of the'ab'sorbing means."

'71An electri'c'al' discharge device adaptedfor' ultra-high frequency use, which comprises an evacuated envelope, means within the envelope for producing groups of electrons traveling at relatively low velocity along a rectilinear path,- means within the envelope including a plurality of electrodes spaced along said path for subject* ing the groups of electrons moving along said path to a constant rectilinear field to accelerate the groups without substantially changing their direction, potential-source means connected to said electrodes for maintaining them at increasing potentials with respect to the means for pro ducing the groups of electrons, means within the envelope beyond the accelerating means and spaced therefrom for absorbing energy from the accelerated groups of electrons, said absorbing means including a cavity resonator having an opening through which the groups of electrons may enter the resonator, and means within the envelope between the group accelerating means and the resonator of the absorbing means for focusing the accelerated groups of electrons as they approach the opening in said resonator.

8. An electrical discharge device adapted for ultra-high frequency use, which comprises an evacuated envelope, means within the envelope for producing groups of charged particles traveling at relatively low velocity along a rectilinear path, a plurality of electrodes mounted on the envelope wall and encircling and spaced along.

the path of the groups of particles, potentialsource means connected to said electrodes for maintaining them .at increasing potentials with ultra-high frequencyuse, which-comprises an evacuated envelopefmeans within the envelope for producing a beam of electrons travelingalong a rectilinear path Within the envelope at relatively low velocity, means for forming the electrons in the beam into groups, said means including a cavity resonator mounted on the wall.

of the envelope and having walls extending across the path of the beam, said resonator walls having openings through which the beam passes,

means for absorbing energy from the groups of electrons, said means including a cavity resonator mounted on the envelope wall and having a wall extending across the path of travel of the" groups of electrons and provided with an opening through which'the groups may enter theresonator,'the walls of the envelope between the resonators being made up of alternate annular sections of'insulation and annular metallic' disc electrodes, and potential-source means connected to said electrodes for maintaining them at increasing potentials with respect to the 'beam producing means 'efi'ectiveto' subject the groups of electronsto a constant rectilinear field accelerating the groups without 'substantiall t' changing their direction.

10.-An electricaldischarge device adapted for ultra-high frequency use, which comprises an evacuated envelope, means Within the envelope for producing a beam of electrons traveling along a .rectilinear path within the 'envelope'at relatively low velocity, means for'forming-the electrons in the beam into groups, said means including a cavity resonator mounted on the wall of the envelope and having Walls extending across the path of the beam, said resonator walls having openings through which the beam passes, and grids in said openings, means for absorbing energy from the groups of electrons, said means including a cavity resonator mounted on the envelope wall and having a Wall extending across tween the resonators, potential-source means connected to said electrodes for maintaining them at successively higher potentials along'the' path of travel of the electrons with respect to the beam-producing means, and means mounted on the envelope Wall between the electrodes and the resonator of the absorbing means for focusing the groups of electrons into the resonator of the absorbing means through said unobstructed opening.

' CAPER'ION B. I-IORS-LEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

